1. Field of the Invention
The present invention relates to an ink jet recording head having a plurality of heat generating elements such possible to be driven independently in a liquid path, and also to ink jet recording method and ink jet recording apparatus utilizing such ink jet recording head.
2. Related Background Art
Most of ink jet recording apparatuses are known as printing devices used in a printer, a facsimile, a word processor, a copying maching and so on. Among such ink jet recording appartatuses, there is already known an appartus utilizing thermal energy as energy for ink discharge so as to generage bubbles and thereby achieve discharge of ink. Recently, this type of ink jet recording apparatus has been known as an ink jet printing apparatus for printing a fixed pattern or design or a synthesized image on the textiles.
The ink jet recording head employed in the above-mentioned ink jet recording apparatus utilizes an electrothermal transducer element (hereinafter called heater) as means for generating thermal energy. The ink jet recording head usually has a configuration with the heater in each ink path (hereinafter called liquid path) (such configuration being hereinafter called single-heater configuration). On the other hand, there is known an ink jet recording head having a configuration with plural heaters in each ink path (hereinafter called multi-heater configuration), for achieving the following objectives.
Firstly, plural heaters are activated (for heat generation) alternately or one by one, in order to extend a service life of the ink jet recording head.
Secondly, plural heaters are employed in order to increase the range of change in an ink discharge amount for reproducing gradation, and the ink discharge amount is varied by selecting the heaters to be activated or determining the number of heaters to be activated.
In the latter case, in a more specific structure, plural heaters are positioned along a discharge direction of ink in an ink path leading to a discharge opening. The ink discharge amount is changed by varying the distance between the respective activated heater and the discharge opening, through the selection of heaters to be activated or the determination of the number of heaters to be activated.
There is also disclosed, as in the Japanese Patent Laid-open Application No. 55-132259, for example, another configuration in which plural heaters of respectively different surface areas are positioned in each ink path, and an ink discharge amount is varied by the selection of heaters to be activated or determination of the number of heaters to be activated.
Among the prior techniques mentioned above, the multi-heater configuration can realize various discharge amounts by shifting a timing of activation of a heater. In order to meet the requirement of higher image quality requested recently to a recording if apparatus, there has been proposed a technique of achieving modulation of a record image by modulating a liquid discharge amount from a discharge opening using the multi-heater configuration. This type of recording apparatus is being gradually commercialized.
In an ink jet recording head with the multi-heater configuration, a liquid discharge amount can be modulated by shifting a timing of activation of a heater. But a certain long is required for shifting the timing. For this reason, it has been relatively difficult to apply the discharge amount modulating technology based on the multi-heater configuration, to a high-speed printer provided with a plurality of discharge nozzles. Also, the configuration of a drive circuit becomes inevitably complex, because drive signals of different timings have to be supplied to heaters provided for each nozzle.
Besides, in case of the discharge amount modulation, an ink discharge speed fluctuates corresponding to the change in the ink discharge amount, whereby a landing position of an ink droplet fluctuates. Also, even in case the discharge amount modulation is not employed, though the ink discharge amount fluctuates little, if an actual timing of activation fluctuates from a predetermined timing, the ink discharge speed fluctuates and thus the landing position of the ink droplet fluctuates. This fluctuation in the landing position of the ink droplet results in deterioration of the image quality.